declaration of estimated tax vs estimated tax return

declaration of estimated tax and estimated tax return both are nouns.

Word	Noun	Adjective	Verb	Adverb
declaration of estimated tax	Yes	No	No	No
estimated tax return	Yes	No	No	No

As nouns, declaration of estimated tax and estimated tax return are synonyms defined as:

declaration of estimated tax and estimated tax return: return required of a taxpayer whose tax withheld from income does not meet the tax liability for the year

declaration of estimated tax (noun)	estimated tax return (noun)
return required of a taxpayer whose tax withheld from income does not meet the tax liability for the year	return required of a taxpayer whose tax withheld from income does not meet the tax liability for the year